Some mobile devices have features for determining a geographic location. For example, a mobile device can include a receiver for receiving signals from a global satellite system (e.g., global positioning system or GPS). The mobile device can determine a geographic location, including latitude and longitude, using the received GPS signals. In many places where a mobile device does not have a line of sight with GPS satellites, GPS location determination can be error prone. For example, a conventional mobile device often fails to determine a location based on GPS signals when the device is inside a building or tunnel. In addition, even if a mobile device has lines of sight with multiple GPS satellites, error margin of GPS location can be in the order of tens of meters. Such error margin may be too large, for example, for determining on which floor of a building the mobile device is located, and in which room of the floor the mobile device is located.